The 2016 Division 4 champions will be playing in the second tier next year after seeing off Tipperary by four points in Thurles yesterday.
Tipp, meanwhile, still have a chance to seal promotion themselves but they’ll have to beat Armagh away from home next weekend in a winner-takes-all clash.
Tipp manager Liam Kearns described Louth as “fairly cynical” but insisted some of their tactics were “part of the game”.
Louth lost two players to black cards and, defending in numbers, they were determined not to let Tipp make headway, by fair means or foul.
Kearns said: “They were fairly cynical. They took Jack Kennedy down as well (in the second-half), when he was going through. Any danger to their goals, rugby tackles were all on”
Tipp paid a price for missed chances, registering 13 wides while Conor Sweeney also smacked a penalty off the upright deep in first-half stoppage time before they retired 0-8 to 0-6 ahead.
Playing against the breeze, Louth still managed to outscore the hosts by 0-10 to 0-4 in the second-half.
Eoin O’Connor led the way with a five-point haul but Louth had ten scorers on the day.
They could have had a goal early in the second-half but Evan Comerford did well to push James Stewart’s effort over the crossbar.
In truth, it was a disappointing Tipp display as they registered just six points from play. They also lost Michael Quinlivan to a second-half black card, while Josh Keane limped off injured after 20 minutes.
Kelly, who buried his mother on Monday said: “The second-half was outstanding. We had a bump last Sunday (against Armagh) which wasn’t good and for the first 35 minutes we carried a hangover from that. In the second 35, we were outstanding. Overall it’s just a very pleasing performance.
"In our first League game in 2016, we played London in Darver, were terrible on the day but got out by a few points. The transformation over the 18 months is huge. Initially when I started, we were voted 28th or 29th in the country. There was no appetite around the county team.
“It wasn’t a nice place to be but now you come to Semple Stadium and beat a team that’s been in the last four of the All-Ireland series and you get promoted to Division 2. It’s great to see.”
E O’Connor 0-5 (1f), Derek Maguire & Dean Maguire 0-2 each, J Bingham, J Stewart, T Durnin, D Byrne, P Smith (f), C McKeever & G McSorley 0-1 each.
C Sweeney 0-4 (3f), M Quinlivan (1f) & L McGrath 0-2 each, J Kennedy, J Keane (f), K O’Halloran (f) & P Austin 0-1 each.
C Lynch; P Rath, P Reilly, J Bingham; Derek Maguire, K Murphy, J Stewart; Dean Maguire, T Durnin; D Byrne, P Smith, B Duffy; C Martin, E O’Connor, S Mulroy.
K Carr for Reilly (b/c 25), G McSorley for Mulroy (41), R Burns for Byrne (b/c 59), R Moore for Durnin (64), C McKeever for Martin (70+3), D Crilly for O’Connor (70+5).
E Comerford; A Campbell, P Codd, W Connors; B Maher, R Kiely, J Feehan; L Casey, J Kennedy; J Keane, K O’Halloran, B Fox; C Sweeney, M Quinlivan, L McGrath.
L Boland for Fox (temp 8-17), P Austin for Keane (inj., 20), K Fahey for Maher (h.t.), L Boland for O’Halloran (59), S O’Connell for Quinlivan (b/c 66).
Padraig O’Sullivan (Kerry).